This invention relates to a belt reinforcing structure for heavy duty tires, more specifically for off-road tires commonly referred to as earthmover tires.
The large off-road pneumatic tires used in heavy construction and earthmoving operations have operating loads and inflation pressures much higher than conventional trucks and lightweight vehicles.
The radial ply earthmover tires exhibit tremendous load-carrying capacity. The very thick rubber tread and the massive amount of rubber in the sidewalls contribute to high heat generated tire issues.
The use of a large steel cord in the carcass ply in combination with steel cords in the belt structure has been a common practice. Tire manufacturers employ a variety of constructions for optimizing the tires"" durability.
A primary concern for the performance of the tire is insuring adequate rubber penetration into the cords is achieved during the manufacture of the belt layers and in subsequent tire vulcanization. Coupled to this better rubber flow is a desire for higher steel mass and improved wire cut resistance to improve the tires"" overall durability.
The prior art belt constructions for such tires have employed steel cords having many filaments of fine or small diameters. A typical construction would have four or more working belt layers and a pair of high elongation wire reinforced layers for the outermost layers located between the tread and the working belts. These tires would have filaments having diameters between 0.15 and 0.265 mm.
One such tire, a 36.00 R51 earthmover tire, employed a wire construction of 7xc3x977xc3x970.25+1 mm featuring a wrap (xe2x80x9c+1xe2x80x9d) to stabilize the construction with an overall unwrapped cord diameter of 2.25 mm. Alternatively, a 5/8/14xc3x970.265+1 super tensile steel wire construction was used with an overall unwrapped cord diameter of 1.6 mm. These very fine diameter filament constructions are very closely packed making it much more difficult for rubber to penetrate into the interior of the cords. As a result the filaments are more susceptible to cutting and frictional wear, particularly with such small diameter filaments.
The present invention uses multiple filament diameters in a 7xc3x977 cord design to increase the filament spacings in the cord, which allows better rubber penetration for improved resistance to corrosion as well as superior cut resistance. The fracture fatigue common in such large filaments is compensated for by the unique construction of the cord that takes advantage of large internal spaces to allow for maximum rubber coating to protect and cushion the filaments against filament-to-filament frictional wear. In addition, the 7xc3x977 cord of the present invention was designed to be stable without the use of a wrap wire. Thus, the wrapless 7xc3x977 construction eliminated the significant wear mechanism between the wrap and the outer filaments of the construction.
A pneumatic radial ply tire has a tread, a carcass, and a belt reinforcing structure. The carcass has a steel cord reinforced radial ply extending from one annular bead to a second annular bead. The belt reinforcing structure lies radially between the tread and the carcass.
The belt reinforcing structure has at least two steel cord reinforced belt layers, two of the belt layers have steel cords having large filaments in the range of 0.3 mm to 0.6 mm in diameter twisted into a seven by seven cord construction. The cords are oriented parallel to each other within the belt layer. Each belt layer has cords directionally oppositely inclined relative to the adjacent belt layer.
The at least two steel cord reinforced belt layers have cords having an overall unwrapped diameter D of 3.0 mm to 4.0 mm.
In one embodiment of the invention at least one of the at least two steel cord reinforced belt layers has a cord construction 1xc3x97(0.40+6xc3x970.365)+6xc3x97(0.365+6xc3x9735); preferably four belt layers employ this cord construction.
In another embodiment the belt reinforcing structure has two belt layers have a cord construction of 1xc3x97(0.40+6xc3x970.365)+6xc3x97(0.365+6xc3x970.35) and two belt layers with a cord construction of 7xc3x97(3+9+15xc3x970.245)+1 HT.
In both these tire constructions it is optionally recommended that an overlay of two layers reinforced by high elongation (HE) wire be employed between the belt layers and the tread. A cord of 4xc3x976xc3x970.265 (HE) can be used for such an overlay as one example.
Definitions
xe2x80x9cAspect ratioxe2x80x9d of the tire means the ratio of its section height (SH) to its section width (SW);
xe2x80x9cAxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d mean lines or directions that are parallel to the axis of rotation of the tire;
xe2x80x9cBeadxe2x80x9d means that part of the tire comprising an annular tensile member wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes, toe guards and chafers, to fit the design rim;
xe2x80x9cBelt reinforcing structurexe2x80x9d means at least two layers of plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 17 degrees to 27 degrees with respect to the equatorial plane of the tire;
xe2x80x9cCarcassxe2x80x9d means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads;
xe2x80x9cCircumferentialxe2x80x9d means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction;
xe2x80x9cChafersxe2x80x9d refers to narrow strips of material placed around the outside of the bead to protect cord plies from the rim, distribute flexing above the rim, and to seal the tire;
xe2x80x9cChippersxe2x80x9d mean a reinforcement structure located in the bead portion of the tire;
xe2x80x9cCordxe2x80x9d means one of the reinforcement strands of which the plies in the tire are comprised;
xe2x80x9cEquatorial plane (EP)xe2x80x9d means the plane perpendicular to the tire""s axis of rotation and passing through the center of its tread;
xe2x80x9cFootprintxe2x80x9d means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under normal load and pressure;
xe2x80x9cInnerlinerxe2x80x9d means the layer or layers of elastomer or other material that form the inside surface of a tubeless tire and that contain the inflating fluid within the tire;
xe2x80x9cNet-to-gross ratioxe2x80x9d means the ratio of the tire tread rubber that makes contact with the road surface while in the footprint, divided by the area of the tread in the footprint, including non-contacting portions such as grooves;
xe2x80x9cNominal rim diameterxe2x80x9d means the average diameter of the rim flange at the location where the bead portion of the tire seats;
xe2x80x9cNormal inflation pressurexe2x80x9d refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire;
xe2x80x9cNormal loadxe2x80x9d refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire;
xe2x80x9cPlyxe2x80x9d means a continuous layer of rubber-coated parallel cords;
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d means directions radially toward or away from the axis of rotation of the tire;
xe2x80x9cRadial-ply tirexe2x80x9d means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65xc2x0 and 90xc2x0 with respect to the equatorial plane of the tire;
xe2x80x9cSection heightxe2x80x9d (SH) means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane.